A diesel engine for switching between a normal combustion mode and a premixed combustion mode according to the operating conditions of the internal combustion engine is described using FIG. 9 (refer to Japanese Laid-Open Publication No. JP 2003-83119A).
In normal combustion mode, fuel is injected from a fuel injection nozzle 2 into a cavity 3 at top of the piston surface at the timing when a piston 1 is near the compression top dead center as in an ordinary engine. In the sample drawing, injection of the fuel begins at any point between BTDC 10° and 0°. In this normal combustion mode, an aspect of diffusion combustion is adopted wherein the fuel injected in the initial stage of fuel injection ignites after an ignition delay time, and fuel is continuously injected into the flame formed thereby, and that fuel combusts. In that diffusion combustion, additional fuel is injected into the flame and combusted, so fuel must be supplied and combusted in a location where oxygen is originally scarce, and smoke is readily generated. The premixed combustion mode described below is therefore used at the same time according to the operating conditions of the engine.
The premixed combustion mode is for injecting fuel from the fuel injection nozzle 2 into the cavity 3 at an earlier timing than the normal combustion mode and at timing when ignition of the fuel occurs after the injection ends. In the sample drawing, the injection of fuel begins at any timing between BTDC 50° and 20°. In this premixed combustion mode, all of the injected fuel is mixed with air and combusts after the interior of the combustion chamber is substantially uniformly rarefied, so combustion occurs in a state with adequate oxygen present in the environs of the fuel, the generation of smoke can be curbed, and the generation of NOx can also be curbed because the combustion rate is relatively slow and the combustion temperature does not rise rapidly.
Patent Document 1: Japanese Patent Application Laid-open No. 2003-83119